Haze Fan, who works for the Bloomberg News bureau in Beijing, was last in contact with one of her editors about 11:30am local time on December 7
The European Union has urged China to release all journalists and citizens held in connection with their reporting, following the detention of a Bloomberg News employee.
Haze Fan, a Chinese citizen, was taken from her home by plain-clothes security officials last Monday, Bloomberg said, and Beijing said she had been detained on suspicion of endangering national security.
“All those arrested and detained in connection with their reporting activity should be immediately released,” an EU spokesperson said in a statement on Saturday.
The statement mentioned that “other Chinese journalists or citizens have disappeared this year, or been detained or harassed after engaging in reporting”.
“We expect the Chinese authorities to grant her (Fan) medical assistance if needed, prompt access to a lawyer of her choice, and contacts with her family,” it added.
The Chinese foreign ministry said earlier that Fan’s case was under investigation.
Bloomberg said it was “very concerned for her” and was continuing to seek more information.
Chinese citizens are forbidden by the government from working as reporters for foreign news organisations in China but are allowed to work as news assistants.
Fan, who joined Bloomberg in 2017, has been credited as a contributor on numerous business stories.
Her detention comes months after China held a high-profile Chinese-born Australian journalist, citing similar suspicions.
Cheng Lei, a TV anchor at Chinese state-owned outlet CGTN, has not been seen in public since being detained.
Two other Australian reporters – Bill Birtles and Michael Smith – fled China shortly after being interrogated about Cheng.